Disruption with some GitHub services
This summary is created by Generative AI and may differ from the actual content.
Overview
On April 22, 2026, from 18:49 to 19:32 UTC, the Copilot Cloud Agent service experienced failures for sessions that used the Agent HQ Codex agent. All entry points for Codex agent sessions (issue assignment, @copilot comment mentions) failed to start, affecting roughly 0.5 % of total Copilot Cloud Agent jobs (~2,000 jobs). Other agents (Copilot and non‑Codex agents) continued to operate normally.
Impact
The incident impacted a small fraction of the service – about 0.5 % of Copilot Cloud Agent jobs, translating to approximately 2,000 failed jobs. No broader user‑facing services were affected, and there was no reported revenue or functional impact beyond the failed Codex agent sessions.
Trigger
A model‑resolution mismatch in the Codex agent sessions caused an incompatible model to be selected at runtime, leading to session start failures.
Detection
Failure of Codex agent sessions was observed as job start errors across all entry points, triggering alerts and on‑call investigation of the degradation.
Resolution
A mitigation was deployed that forces the selection of a stable default model for Codex agent sessions, restoring functionality. Additionally, a plan to harden the model‑resolution path to correctly scope supported models for each agent is underway.
Root Cause
A bug in the model‑resolution logic caused the Codex agent to receive an incompatible model at runtime, resulting in the observed session failures.